diff --git a/Lib/fontTools/merge.py b/Lib/fontTools/merge.py
index 8e212ec..fe61f94 100644
--- a/Lib/fontTools/merge.py
+++ b/Lib/fontTools/merge.py
@@ -260,9 +260,9 @@
 	'sTypoLineGap': max,
 	'usWinAscent': max,
 	'usWinDescent': max,
-	'ulCodePageRange1': bitwise_or,
-	'ulCodePageRange2': bitwise_or,
-	'usMaxContex': max,
+	'ulCodePageRange1': onlyExisting(bitwise_or),
+	'ulCodePageRange2': onlyExisting(bitwise_or),
+	'usMaxContex': onlyExisting(max),
 	# TODO version 5
 }